1. Field of the Invention
The present invention relates to an automotive alternator, and more particularly, to improvement of a stator.
2. Description of the Related Art
FIG. 15 is a sectional view showing a conventional automotive alternator. The alternator includes a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2, a rotating shaft 6, a rotating shaft 6 accommodated in the case 3 and having a pulley 4 fixed to an end thereof, a Lundell-type rotor 7 fixed to the rotating shaft 6, cooling fans 5 fixed at both the sides of the rotor 7, a stator 8 fixed at the inner wall surface in the case 3, slip rings 9 fixed at the other end of the rotating shaft 6 for supplying current to the rotor 7, a pair of brushes 10 in sliding contact with the slip rings 9, a brush holder 11 in which the brushes 10 are housed, rectifiers 12 electrically connected to the stator 8 for converting alternate current generated in the stator 8 to direct current, a heat sink 17 fitted at the brush holder, and a regulator 18 adhered to the heat sink 17 for regulating the magnitude of AC voltage generated by the stator 8.
The rotor 7 includes a rotor coil 13 for generating magnetic flux on passage of electric current and a pole core 14 disposed so as to cover the rotor coil 13, magnetic poles being formed by magnetic flux generated in the rotor coil 13. The pole core 14 is composed of a pair of a first pole core member 21 and a second pole core member 22 which are meshed with each other. The first pole core member 21 and the second pole core member 22 are made of iron, each has claw-shaped magnetic poles 23 and 24.
The stator 8 includes a stator core 15, and a stator coil 16 in which alternate current is generated by the change of magnetic flux from the rotor coil 13 as the rotor 7, which has a conductive wire wound around the stator core 15, rotates.
In the automotive alternator constructed as described above, electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13, generating magnetic flux. The claw-shaped magnetic poles 23 of the first pole core member 21 are magnetized with north seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 24 of the second pole core member 22 are magnetized with south-seeking (S) poles. At the same time, the pulley 4 is driven by an engine and the rotor 7 is rotated by the rotating shaft 6. Thus, a rotating magnetic field is applied to the stator coil 16, generating electromotive force in the stator coil 16. This alternating electromotive force passes through the rectifiers 12 and is rectified to direct current, the output voltage of the rectifiers 12 is regulated by the regulator 18, and the battery is recharged.
The cooling air flow generated by the cooling fans 5 is sucked in from the air intake vents 1a and 2a of the front and rear brackets 1 and 2, cools the rectifiers 12 and the regulator 18 as heating members passing therethrough at a rear end and further cools the front-end and rear-end coil ends 16a and 16b of the stator coil passing through the blades 51 of the respective fans from the inner diameter side to the outside diameter side thereof, and is discharged from the air discharge vents 1b and 2b of the front and rear brackets 1 and 2. That is, the coil ends 16a and 16b of the stator coil 16, which generate a large amount of heat and influence an output capability when heated to high temperature, are interposed between the blades 51 and the air discharge vents 1b and 2b of the front and rear brackets 1 and 2 so as to be reliably cooled.
In the stator 8, the rear side of an approximately-U-shaped segment 31 is molded in a tortoise shell shape (bent at three positions) and inserted into the stator core 15 as shown in FIG. 16. Thus, the coil ends 16a and 16b are bent back at the extreme end of the U-shaped bent portion inclined with respect to the rotating shaft 6 linearly from the root thereof projecting from the stator core 15 to the extreme end thereof so that adjacent segments 31 are neatly arranged without overlapping with each other. With the above construction, the stator 8 has the same shape over substantially the overall circumference thereof and is constructed very neatly.
In the stator constructed as described above, both the sides of the U-shaped portion of an approximately U-shaped segment 31 are inserted into one of the slots 15a of the stator core 15 from the lower side of the figure as shown in FIG. 16, and the ends of the U-shaped segment 31, which project upward from the stator core 15 in the figure, are bent and then jointed to the ends of other U-shaped segment 31, thereby forming a stator winding. In conventional automotive alternators, the average amount of application per unit area of the varnish, with which the joint-side coil end 16a of an U-shaped segment 31 is impregnated, is the same as the average amount of application per unit area of the varnish, with which the curved turn-side (counter-joint-side) coil end 16b of the U-shaped segment 31.
Further, in other example of the stator of conventional automotive alternators, both the coil ends 16a and 16b are impregnated with no varnish.
When the stator of the automotive alternator constructed as described above is impregnated with no varnish, insulation is lost between respective coil pieces on a joint-side thereof having no insulation film, by which an output is dropped by short-circuit and magnetic noise is deteriorated.
Further, when the coil ends 16a and 16b are not impregnated with varnish, the inner circumferential surfaces of the coil ends are made uneven by the windings arranged in a circumferential direction. Thus, there is arisen a problem that interference noise is generated by the rotation of the claw-shaped magnetic poles of the rotor 7 and the rotation of the fan 5.
In contrast, when both the coil ends 16a and 16b are impregnated with varnish in the same amount, the turn-side coil end 16b, whose insulation is not substantially lost, is impregnated with varnish similarly, which increases an amount of impregnation of varnish and a cost is increased accordingly. Further, the cooling property of the stator 8 is lowered by an increase in an amount of impregnation of varnish.
Furthermore, in the bent and jointed coil end, a load due to residual stress, which is generated when the segments are bent and deformed, is applied to the coil end. However, when a small amount of varnish is applied to the coil end, it is vibrated because it has a small amount of mechanical fastening force and a small amount of rigidity, noise being caused by the vibration of it and the insulation film of the coil end being exfoliated thereby.